The present invention relates to a leveling system for a vehicle, and more particularly to a height control valve for use with such a leveling system.
It is common practice to provide automotive vehicles with leveling systems that automatically adjust the suspension of the vehicle to compensate for various load conditions. These systems are installed in a wide variety of vehicles ranging from passenger cars to semi-trucks and semi-trailers. A conventional leveling system includes pneumatic suspension elements, such as shocks or air springs, that can be inflated or deflated to control the height of the frame with respect to the axle. For example, with semi-trailers, heavy loads can cause the suspension to sag, thereby decreasing the distance between the frame and the axle. Further, if the load is not evenly distributed throughout the trailer, the load may also alter the attitude of the trailer (e.g. fore-aft tilt and/or side-to-side tilt). These conditions can adversely affect the handling of the trailer, and can even result in damage to the suspension, frame, and/or axle. With conventional leveling systems, this problem is addressed by inflating the pneumatic suspension to compensate for the load. Specifically, when the attitude of the trailer has been affected by an uneven load, the various suspension elements can be inflated or deflated independently to return the trailer to the desired attitude.
In many leveling systems, the height of the suspension is automatically controlled by mechanical height control valves. Height control valves are typically located within the leveling circuit between the source of compressed air and the suspension elements. When the distance between the axle and frame falls below the desired position, the height control automatically causes inflation of the suspension, and when the distance between the axle and the frame is too great, the height control valve automatically causes the suspension to bleed or deflate. Many conventional systems include a separate height control valve at each axle. This permits separate control of the suspension at each axle which in turn permits the suspension to compensate for fore-aft tilt. Other systems include separate suspension elements and separate height control valves at each end of each axle. These more complicated systems permit compensation for side-to-side tilt as well as fore-aft tilt.
A conventional height control valve typically includes a valve body and a control arm. The valve body is generally mounted directly to the vehicle frame and contains a valve assembly which controls the flow of air through the valve. The control arm extends from the valve body to the axle, and is operatively connected to the valve assembly by an actuator mechanism. In a conventional system, the control arm is capable of moving the valve between three distinct positions. First, when in the upward (or "supply") position, the control arm manipulates the valve assembly to permit air to inflate the suspension. Second, when in the downward (or "exhaust") position, the control arm manipulates the valve assembly to permit air to bleed from the suspension. And finally, when in the central (or "closed") position, the control arm manipulates the valve assembly to prevent air from entering or exiting the suspension.
Conventional height control valves suffer from a variety of distinct problems. First, the components of the valve assembly are assembled directly within the valve body. As a result, assembly and quality control inspection of the valve assembly are relatively difficult to perform. Second, the valve assembly is readily accessible making it easy for unauthorized and potentially dangerous modifications to be made to the valve. And third, exhaust air from the suspension can drive dirt and other debris into the valve assembly and actuator mechanism where it can reduce the overall life of the valve and adversely affect its operation.